Caricature of Charles Darwin from The Hornet, ca. 1871.

Rejecting evolutionary psychology (EP) is tantamount to rejecting evolution. Or so goes the argument put forward by evolutionary psychologist Glenn Geher in a recent Psychology Today editorial. As Geher writes, there does seem to be some disconnect involved in accepting evolution, on the one hand, and rejecting evolutionary psychology on the other. It’s the sort of about-face that seems dependent on a certain amount of cognitive dissonance. For many – particularly in the humanities and social sciences – this incongruence is probably very often politically or ideologically motivated. Rightly uncomfortable with the sort of late 19^th and early 20^th century typological thinking – sometimes crudely justified by a slipshod invocation of Darwinian ideas – that contributed to classist and racist social agendas, many rebel against the notion that human behavior is biologically determined.

This is peculiar for a number of reasons. For one, it seems to demand either a rejection of all Darwinian accounts of behavior or a vaguely vitalistic assertion that human behavior is governed by forces distinctly different from those that shape the behavior of other animals. The problem here is that the differences between humans and our animal cousins are largely differences of degree, not of kind. This leaves the task of identifying the point at which an organism becomes a creature ungoverned by fitness-enhancing imperatives a matter of arbitration.

To the extent that Geher is rebutting the position represented by the Standard Social Science Model, I tend to agree with him. For many, the notion that humans are more or less infinitely plastic hasn’t lost its allure. It is, after all, appealing to think that we are born a blank slate. Unfortunately, this is mostly a product of wishful thinking.

For better or worse, humans do share an array of motivations, preferences, and inclinations that are the products of natural selection. Which gets to the more interesting area where Geher might be wrong, or – at least – not entirely right, in his assertion that rejecting evolutionary psychology is equivalent to rejecting evolution. True, the rejection of EP among certain segments of the humanities and social sciences involves a liberal seasoning of cognitive dissonance. But there are also reasons why individuals with an understanding of evolutionary theory and confidence in its ability to unify biological and behavioral phenomena under a single explanatory umbrella might find EP wanting.

On a proximate level, EP seems to fall short of fully explaining the clearly context sensitive expression of human universals, much less the social, ecological, and epigenetic factors that contribute to behavioral diversity. Evolutionary psychology can expose the roots of phenomena like male aggression by pointing to male-male status competition and differential reproductive success (Wrangham & Peterson 1996; Daly & Wilson 1988). But any given case of male violence is contingent upon a variety of environmental factors. In an important sense, placing the explanatory onus on fitness – and therefore the transmission of genetic information – seems to ignore the central dogma of molecular biology. Segments of DNA are transcribed into corresponding strands of RNA which code for protein synthesis, culminating – in terms of behavior – in the production of hormones like testosterone and cortisol that contribute to patterns of aggression. This is a simplification, but the basic point is this: the chain of causation between genes and behavior is long and complicated, and can only be understood probabilistically. Serious evolutionary psychologists are aware of this, recognizing that behavior unfolds at the interface between environmental and genetic inputs. Yet, by placing their emphasis on behavioral adaptation and, implicitly, the genetic variation underlying traits, evolutionary psychologists give short-shrift to other important factors.

The disconnect between biological adaptation and behavior is particularly pronounced in the concept of massive modularity. The massive modularity hypothesis posits that individual behaviors are the product of specialized cognitive algorithms that exist explicitly because they conferred some fitness advantage on members of an ancestral population (Tooby & Cosmides 1992). The actual degree of modularity – if any – exhibited by the human mind is a thorny question, far from being resolved. Here, suffice it to say that I’m skeptical that the modularity of the human mind can be properly described as massive or that modularity is necessary to explain most human behaviors. As a heuristic for thinking about the evolutionary roots of behavior and formulating adaptationist hypotheses, modularity has some utility. But as a firm conceptualization of how the mind actually works, it lacks clear empirical support. Neurologically, there is little evidence for the existence of structures corresponding to the cognitive algorithms suggested by modularity. There is no reason to presume that human universals like cooperation or theory of mind need to be accompanied by a corresponding set of specialized cognitive modules. Furthermore, the notion of massive modularity seems to impose a level of rigidity that defies what we know about human behavioral plasticity and ignores the likely crucial but currently poorly understood influence of epigenetic changes. Evolutionary psychologists have countered this argument with a metaphor involving a globe-trotting, context sensitive jukebox, but this argument doesn’t yield any predictions that are sufficient to distinguish it from alternatives (Ermer et al. 2007).

Much explanatory work can in fact be done without assuming the burden of such a highly specialized cognitive architecture. This is particularly true when it comes down to thinking explicitly about the components of humanity’s evolved psychology. Our remarkable facility with social learning, for instance, is very likely the product of natural selection. In concert with our capacity for language – an evolved trait, for sure, though not necessarily an adaptation – social learning provides a generalized mechanism that has served as a scaffold for behaviors shaped by the accumulation and transmission of social information (Alvard 2003; Sterelny 2003). Examples such as this go a long way toward illustrating one of the primary deficits of the EP program: a broad failure to take into account the multiple scales of information that contribute to the construction of the behavior researchers are trying to explain. The genes we inherit from our parents, present in their germ line because of the role they have typically played in building reproductively successful phenotypes, only partially explain any given trait. Maternal effects and environmentally induced epigenetic changes throughout growth and development are crucial. Some behaviors are likely adaptations in precisely the sense intended by evolutionary psychologists, but others involve the dynamic interaction between ecological and social sources of information – places where the boundary between adaptation and non-adaptive plasticity (i.e. plasticity not explicable in terms of heritable genetic information) gets fuzzy.

Critics of EP have also occasionally charged its proponents with being overly adaptationist, in the pejorative sense of the term outlined by Stephen Jay Gould and Richard Lewontin in their 1979 paper, “The Spandrels of San Marco”. I’m typically sympathetic to the adaptationist perspective and find some of the arguments put forward by Gould and Lewontin less than convincing, but in the case of evolutionary psychology, the central criticism is frequently valid. In an exercise limited only by the bounds of imagination, evolutionary psychologists posit the existence of some cognitive adaptation then postulate a set of plausible circumstances that would have selected for it among the mobile bands of foragers ancestral to modern humans. The problem here is twofold. First, testing adaptationist hypotheses can be tricky. In the strict, historical sense of the term, for a trait to be an adaptation it must have a genetic component that proliferated because it contributed to a good solution to a given adaptive challenge, such that it conferred higher fitness on its bearers than conspecifics lacking said trait (Sober 1984). Unfortunately, the adaptive challenges that shaped the trait are, by definition, in the past. If environments have been more or less stable from the point at which the trait became a fixed feature of the population and the point at which the trait is observed, this isn’t much of problem. But if things have changed over the intervening years, researchers are confronted with the issue of adaptive lag  – a result of a disparity between extant circumstances and the circumstances that selected for the trait (Laland & Brown 2006; Dawkins 1982). If adaptations are identified by the increased reproductive success they facilitate relative to a specific set of selective pressures and said pressures are no longer at work, empirically demonstrating adaptation can prove difficult. Evolutionary psychologists are thus left with ubiquity and the appearance of “design” (reasonable, because natural selection is the primary force responsible for the appearance of design in biological systems) as criteria for identifying psychological adaptations. These are heuristics that might point researchers in useful directions, but they do not provide unequivocal measures of adaptation.

The second problem extends from first. Sometimes the distinguishing characteristic of adaptation is the point in time at which the trait in question evolved. Invoking adaptive explanations is most useful when accompanied by an understanding of the conditions that selected for the trait in question. This makes distinguishing between ancestrally derived and uniquely acquired characteristic essential (Thornhill 2007). At some point, many of the features of the general body plan shared by all tetrapods (amphibians, reptiles, mammals, and birds) were probably adaptations. But these homologous traits evolved as adaptations at some point well before the emergence of any of the aforementioned classes of animals. This is an extreme example, but it points to another flaw in certain veins of EP. Consider, for purposes of illustration, the problem of cheater detection. It has been hypothesized that humans should have some ability to detect individuals likely to defect from social contracts, because these individuals represent free-riders imposing costs on the cooperators they’ve duped. In other words, humans should be able to identify cheaters (Cosmides & Tooby 1992). This is quite reasonable, and, I think, probably true. It also might not be an exclusively human trait, because its advantages should be present whenever survival and reproduction depends on participations within a larger social unit. Considering the amount of cooperating humans do with non-kin, cheater detection may be more elaborated in our line, but it ought to be present in other primates as well.

The problem is not whether human psychology and behavior has been shaped by evolutionary processes. It clearly has, so in that sense EP is based on a truism. There are, of course, those who take issue with this. The distinguished anthropologist Marshall Sahlins, for instance, has spilled considerable ink railing against attempts to develop evolutionary explanations for human behavior, adopting the curious tactic of arguing that evolutionary explanations are false by demonstrating an apparent inability to understand any of them.

The real question is whether or not human behavior has been shaped by evolution in the manner conceived by evolutionary psychologists. There isn’t really an unequivocal answer in this regard, but there is plenty of room for skepticism. Though attempts to formulate Darwinian explanations for human behavior date back to at least Darwin himself, a relatively recent proliferation of interest has spawned a number of variously competing and complimentary paradigms. This is a good thing, encouraging the kind of discourse that fuels scientific progress. Though EP has deservedly gained some traction, it’s still too early to dismiss all of its detractors as victims of the sort of tortured intellectual gymnastics exemplified by the proponents of the Standard Social Science Model. Serious evolutionists can – and in many cases should – take issue with a number of the claims leveled by EP without running the risk of being dismissed as intellectual charlatans.

Ultimately, what we are trying to explain through the application of a theoretical paradigm like EP is phenotypes. It should be unsurprising then that an understanding of the forces that selected for specific adaptations in past environments, the adaptive challenges that shaped them into universal components of human phenotypes, can only teach us so much. This point is enhanced when one recognizes that many behaviors aren’t necessarily explicable in the adaptive sense at the heart of the EP program. Behavior is one of those phenomena for which the most interesting explanations might often reside at the proximate end of the explanatory spectrum. This isn’t an anti-Darwinian position. The neo-Darwinian synthesis provides an exceptionally powerful toolkit for understanding and explaining behavior. Maybe, I’d venture to say, one the best. But as our understanding of evolutionary processes deepens, it becomes more and more apparent that there is more at work in shaping phenotypes than the genes that proliferated because of their role in building fit phenotypes in ancestral environments.

References:

Alvard, Michael S. 2003. The adaptive nature of culture. Evolutionary Anthropology. Evolutionary Anthropology 12:136–149

Cosmides, Leda and John Tooby. 1992  Cognitive Adaptations for Social Exchange. In The Adapted Mind: Evolutionary Psychology and the Generation of Culture. Jerome H. Barkow, Leda Cosmides, & John Tooby eds. Pp. 161-228. New York: Oxford University Press.

Daly, Martin and Margo Wilson. 1988  Homicide. Aldine Transaction

Dawkins, Richard. 1982. The Extended Phenotype: the Long Reach of the Gene. Oxford University Press: New York

Ermer, Elsa., Leda Cosmides, and John Tooby. 2007  Functional Specialization and the Adaptationist Program. In The Evolution of Mind. Steven W. Gangestad & Jeffry A. Simpson eds. Pp. 153-160. New York: The Guilford Press.

Gould, Stephen Jay and Richard C. Lewontin. 1979. The spandrels of San Marco and the Panglossian paradigm: a critique of the         adaptationist programme. Proceedings of the Royal Society B. 209: 581-598

Laland, Kevin N. & Gillian R. Brown. 2006. Niche construction, human behavior, and the adaptive-lag hypothesis. Evolutionary Anthropology. 15: 95-104

Newcombe, Nora S., Kristin R. Ratliff, Wendy L. Shallcross, and Alexandra Thyman.2009  Is Cognitive Modularity Necessary in an Evolutionary Account of Development? In Cognitive Biology: Evolutionary and Developmental Perspective on Mind, Brain, and Behavior. Luca Tommas, Mary A. Peterson, & Lynn Nadel eds. Pp. 105-126. Cambridge, MA; MIT Press.

Sober, Elliott. 1984. The Nature of Selection. MIT Press.

Sterelny, Kim. 2003. Thought in a Hostile World: The Evolution of Human Cognition. Malden, MA: Blackwell Publishing

Thornhill, Randy. 2007  Comprehensive knowledge of human evolutionary history requires both adaptationism and phylogenetics. In The Evolution of Mind. Steven W. Gangestad & Jeffry. A. Simpson eds. Pp. 31-37. New York: The Guilford Press.

Tooby, John. and Leda Cosmides. 1992 Psychological foundations of culture. In The Adapted Mind: Evolutionary Psychology and the Generation of Culture. Jerome H. Barkow, Leda Cosmides, & John Tooby eds. Pp. 19-136. New York: Oxford University Press.

Wrangham, Richard and Dale Peterson. 1996  Demonic Males: Apes and the Origins of Human Violence. New York, NY: Houghton Mifflin Company.